|
Magnetomotive Force
In physics, the magnetomotive force (mmf) is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, often called Ohm's law for magnetic circuits. It is the property of certain substances or phenomena that give rise to magnetic fields: \mathcal = \Phi \mathcal , where is the magnetic flux and \mathcal is the reluctance of the circuit. It can be seen that the magnetomotive force plays a role in this equation analogous to the voltage in Ohm's law: , since it is the cause of magnetic flux in a magnetic circuit: # \mathcal = NI where is the number of turns in the coil and is the electric current through the circuit. # \mathcal = \Phi \mathcal where is the magnetic flux and \mathcal is the magnetic reluctance # \mathcal = HL where is the magnetizing force (the strength of the magnetizing field) and is the mean length of a solenoid or the circumference of a toroid. Units The SI unit of mmf is the ampere, the same as the unit of current (analogou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events." Physics is one of the most fundamental scientific disciplines, with its main goal being to understand how the universe behaves. "Physics is one of the most fundamental of the sciences. Scientists of all disciplines use the ideas of physics, including chemists who study the structure of molecules, paleontologists who try to reconstruct how dinosaurs walked, and climatologists who study how human activities affect the atmosphere and oceans. Physics is also the foundation of all engineering and technology. No engineer could design a flat-screen TV, an interplanetary spacecraft, or even a better mousetrap without first understanding the basic laws of physic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named ''volt''. The voltage between points can be caused by the build-up of electric charge (e.g., a capacitor), and from an electromotive force (e.g., electromagnetic induction in generator, inductors, and transformers). On a macroscopic scale, a potential difference can be caused by electrochemical processes (e.g., cells and batteries), the pressure-induced piezoelectric effect, and the thermoelectric effect. A voltmeter can be used to measure the voltage between two points in a system. Often a common reference potential such as the ground of the system is used as one of the points. A voltage can represent either a source ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetism
Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is one aspect of the combined phenomena of electromagnetism. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron, cobalt, and nickel and their alloys. The rare-earth metals neodymium and samarium are less common examples. The prefix ' refers to iron because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, Fe3O4. All substances exhibit some type of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silvanus P
Silvanus or Sylvanus may refer to: *Silas (Silvanus), disciple, mentioned in four New Testament epistles * Silvanus (monk), one of the Desert Fathers *Silvanus of the Seventy, a traditional figure in Eastern Orthodox tradition assumed to be one of the Seventy Apostles *Silvanus (mythology), a Roman tutelary deity or spirit of woods and fields *Silvanus (name), a surname and given name (and list of people with the name) * Silvanus (''Forgotten Realms''), a fictional deity in the ''Forgotten Realms'' setting of ''Dungeons & Dragons'' * Sylvanus, Michigan, a village * ''Silvanus'' (genus), a genus of beetles See also *''Teachings of Silvanus'', a text from the Nag Hammadi library * Sylvanus Selleck Gristmill, a gristmill built in 1796 in Greenwich, Connecticut * Sylvanus Thayer Award, an award that is given each year by the United States Military Academy at West Point *Silvain (other) *Silvan (other) *Sylvain (other) Sylvain is the French form of Silvanus. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Hopkinson
John Hopkinson, FRS, (27 July 1849 – 27 August 1898) was a British physicist, electrical engineer, Fellow of the Royal Society and President of the IEE (now the IET) twice in 1890 and 1896. He invented the three-wire (three-phase) system for the distribution of electrical power, for which he was granted a patent in 1882. He also worked in many areas of electromagnetism and electrostatics, and in 1890 was appointed professor of electrical engineering at King's College London, where he was also director of the Siemens Laboratory. Hopkinson's law, the magnetic counterpart to Ohm's law, is named after him. Life and career John Hopkinson was born in Manchester, the eldest of 5 children. His father, also called John, was a mechanical engineer. He was educated at Queenwood School in Hampshire and Owens College in Manchester. He won a scholarship to Trinity College, Cambridge in 1867 and graduated in 1871 as Senior Wrangler, having placed first in the demanding Cambridge Mathemati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James Clerk Maxwell
James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and scientist responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and light as different manifestations of the same phenomenon. Maxwell's equations for electromagnetism have been called the " second great unification in physics" where the first one had been realised by Isaac Newton. With the publication of "A Dynamical Theory of the Electromagnetic Field" in 1865, Maxwell demonstrated that electric and magnetic fields travel through space as waves moving at the speed of light. He proposed that light is an undulation in the same medium that is the cause of electric and magnetic phenomena. (This article accompanied an 8 December 1864 presentation by Maxwell to the Royal Society. His statement that "light and magnetism are affections of the same substance" is at page 499.) The unification of light and electrical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Michael Faraday
Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, diamagnetism and electrolysis. Although Faraday received little formal education, he was one of the most influential scientists in history. It was by his research on the magnetic field around a conductor carrying a direct current that Faraday established the concept of the electromagnetic field in physics. Faraday also established that magnetism could affect rays of light and that there was an underlying relationship between the two phenomena.. the 1911 Encyclopædia Britannica. He similarly discovered the principles of electromagnetic induction, diamagnetism, and the laws of electrolysis. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, and it was largely due to his efforts t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromotive Force
In electromagnetism and electronics, electromotive force (also electromotance, abbreviated emf, denoted \mathcal or ) is an energy transfer to an electric circuit per unit of electric charge, measured in volts. Devices called electrical ''transducers'' provide an emf by converting other forms of energy into electrical energy. Other electrical equipment also produce an emf, such as batteries, which convert chemical energy, and generators, which convert mechanical energy. This energy conversion is achieved by physical forces applying physical work on electric charges. However, electromotive force itself is not a physical force, and for the current ISO/IEC standards consider the term deprecated, favoring the names source voltage or source tension instead (denoted U_s). An electronic–hydraulic analogy may view emf as the mechanical work done to water by a pump, which results in a pressure difference (analogous to voltage). In electromagnetic induction, emf can be defined ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Henry Augustus Rowland
Henry Augustus Rowland (November 27, 1848 – April 16, 1901) was an American physicist and Johns Hopkins educator. Between 1899 and 1901 he served as the first president of the American Physical Society. He is remembered primarily for the high quality of the diffraction gratings he made and for the work he did with them on the solar spectrum. Early life, family and education Rowland was born in Honesdale, Pennsylvania, where his father Henry Augustus Rowland was a Presbyterian pastor. From an early age, the younger Rowland exhibited marked scientific tastes and spent his spare time in electrical and chemical experiments. He graduated from Rensselaer Polytechnic Institute in Troy, New York in 1870. Career After college, Rowland worked for the Western New York railway, but he did not like the work. He became an instructor in natural science at the University of Wooster in Wooster, Ohio. He resigned in order to return to Troy as assistant professor of physics at Rensselaer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gilbert (unit)
The gilbert (symbol: Gb) is an obsolete unit used in practical cgs and CGS-EMU systems to measure magnetomotive force. The unit is named for English physicist William Gilbert. Definition: *1 Gb = (1/4π) Bi-turn Conversion to the corresponding quantity in the SI, with the unit ampere-turn The ampere-turn (A⋅t) is the MKS (metre–kilogram–second) unit of magnetomotive force (MMF), represented by a direct current of one ampere flowing in a single-turn loop in a vacuum. " Turns" refers to the winding number of an electrical con ...: *1 Gb ≘ (10/4π) A-turn ≈ 0.7957747 A-turn *1 A-turn ≘ 4π × 10−1 Gb References {{CGS units Magnetism Units of measurement Centimetre–gram–second system of units ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MKS System
The MKS system of units is a physical system of measurement that uses the metre, kilogram, and second (MKS) as base units. It forms the base of the International System of Units (SI), though SI has since been redefined by different fundamental constants. History By the 19th century, there was a demand by scientists to define a coherent system of units. A coherent system of units is a system of units where all units are directly derived from a set of base units, without the need of any conversion factors. The United States customary units are an example of a non-coherent set of units. In 1874, the British Association for the Advancement of Science (BAAS) introduced the CGS system, a coherent system based on the centimetre, gram and second. These units were inconvenient for electromagnetic applications, since electromagnetic units derived from these did not correspond to the commonly used ''practical units'', such as the volt, ampere and ohm. After the Metre Convention of 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
